The present invention relates generally to two-stroke operating cycle engines and, more particularly, to a two-stroke engine fuel injection system and control system therefor which are adapted for extreme weather conditions.
Two-stroke operating cycle engines (two-cycle engines), although less fuel-efficient than four-stroke operating cycle engines (four-cycle engines), are capable of developing greater horsepower and torque than a comparably-sized four-cycle engine. This feature has led to the use of two-cycle engines in many environments in which operating efficiency is secondary to torque and weight considerations.
Electronically-controlled fuel injection is widely used in four-cycle engines. In electronic fuel injection used in four-cycle engines, sensor readings associated with various engine operating parameters are used to calculate an optimum fuel/air mixture for the engine. Fuel is then injected directly into the engine's cylinders in the proper amount based upon this electronically determined fuel/air mixture. In some four-cycle engine fuel injection systems, the fuel is injected into an air plenum upstream of the cylinder and is subsequently allowed to enter the cylinder with the plenum air through operation of an intake valve. Electronic fuel injection systems have replaced conventional carburetors in many four-cycle engines, especially in the automotive industry. However, fuel injection is not in general use with two-cycle engines and has not heretofore been used with small-displacement two-cycle engines which are used under severe cold weather conditions, for a number of reasons. Small two-cycle engines are used in association with equipment that is relatively inexpensive as compared to automobiles and other machines with which electronic fuel injection has been widely used in the past. In relatively large, expensive machinery, the cost associated with modifying basic engine components to enable internal mounting of various engine parameter sensors may be justified by increased fuel savings and engine performance and may amount to a relatively small portion of the purchase price of such an automobile, etc. In smaller engine environments, the cost of internal engine modification to existing engine assemblies would, in most cases, far outweigh any fuel savings which might be achieved by an electronic fuel injection unit and would represent a substantial increase in the cost of the associated small machine, e.g. snowmobile, dirt bike, etc., powered by the two-cycle engine.
Fuel injection systems without electronic controls have been used on two-cycle engines, but have not been satisfactory on small-displacement, small-mass two-cycle engines. The reason that fuel injection without electronic control has not been used successfully in small two-cycle engines is that such engines lack flywheels and other high-mass rotating components which tend to stabilize engine operation. Due to this lack of a large rotating mass in such engines, even a short duration mismatch between the rate at which fuel is actually delivered to the engine and the optimum engine fuel rate requirements will cause engine sputter or rapid deceleration and stalling. Small, two-cycle engines are especially subject to malfunction under variable operating conditions such as changes in sea level, with associated barometric changes and changes in ambient air temperature. Many machines such as snowmobiles, snowblowers, dirt bikes, etc., are operated in such widely variable operating conditions. In view of the costs associated with engine modification for sensors' need for electronic control of fuel injectors and in view of the fact that the engine parameters which are critical to control of fuel injectors for two-cycle engines were not, prior to the present invention, understood in the art, a successful electronically-controlled fuel injection system for small, two-cycle engines which are subject to extremes in operating conditions has not been developed in the prior art.